1. Field of the Invention
The present invention relates to gauging means, and more particularly to apparatus for determining the relative position or change of position of an object under test.
2. Description of the Prior Art
Heretofore, there have been provided various types of devices for effecting a gauging of the numerous aspects of measuring and testing the mechanical properties of an object under test. These have been in the form of mechanical feeler guages, with accompanying mechanical metering, for checking run-out, or eccentricity of a rotatable member. Such feeler gauges have also been employed to determine dimensional features. Mechanical feelers of that type have the disadvantage of relative inaccuracies resulting from relatively low frequency response when used to determine run-out on a rotating member. For use with a static body, the mechanical metering means have an inherently limited accuracy and sensitivity from the mechanical nature of the system. Further, there are numerous instances wherein it is not desirable to physically touch the object under test. A contacting gauge under such conditions would be harmful to the object.
Alternatively, there have been provided, heretofore, optical sensors as gauges for dimensional determinations. Such optical gauges are exemplified by several patents issued to Samuel C. Hurley, Jr., namely, U.S. Pat. Nos. 2,415,174; 2,415,175; 2,415,176; 2,415,177; 2,415,178; 2,415,179. These patents relate to a means for determining whether or not an object under test matches prescribed dimensions within established tolerances. Because they rely on the illumination or obfuscation of one or more pairs of spaced photodetectors, the relative sensitivity and/or accuracy of such optical systems are necessarily limited.
In another optical sensing device, a single light source and a single photodetector are used to detect deformation of a human eyeball as a means of detecting glaucoma. That device is shown in U.S. Pat. No. 3,304,769 issued to the present inventor. For precise measurements, the power supply for the light source as well as the associated electronic circuitry must be highly regulated in order to avoid errors due to electrical variations.